K-152 Nerpa accident

At the time of the accident, Nerpa was undergoing sea trials at the Russian Pacific Fleet's test range in Peter the Great Gulf, an inlet of the Sea of Japan adjoining the coast of Russia's Primorski Krai province. The vessel had not yet been commissioned by the Russian Navy and was undergoing plant tests under the supervision of a team from the Amur shipyard.[3] For this reason, it had a much larger than usual complement aboard, totaling 208 people, 81 military personnel and 127 civilian engineers from the shipyards responsible for building and outfitting the submarine.[4]

The accident occurred at 8:30 pm local time on 8 November 2008,[5] during the submarine's first underwater test run.[3] The submarine's fire extinguishing system was triggered, sealing two forward compartments and filling them with R-114B2 gas (dibromotetrafluoroethane, known as khladon in Russian).[6] The gas, a haloalkane refrigerant, is used in the Russian Navy's LOKh (lodochnaya obyemnaya khimischeskaya – "submarine volumetric chemical") fire-suppressant system. Each compartment of a Russian submarine contains a LOKh station from which the gas can be delivered into that or adjacent compartments.[7] The gas displaces oxygen and chemically interferes with combustion, enabling it to extinguish fires rapidly in enclosed spaces. In high concentrations, it can cause narcosis, which progresses by stages into excitation, mental confusion, lethargy, and ultimately asphyxiation.[4]

Twenty people died of asphyxiation in the accident. The number of injured was initially put at 21[8] but was later revised to 41 by the Amurskiy Shipbuilding Company, some of whose employees were among the injured. Many of the injured were reported to have suffered from frostbite caused by the chilling effect of the gas.[9]

Following the incident, the Udaloy-class destroyer Admiral Tributs and the rescue vessel Sayany were dispatched from Vladivostok to provide assistance to the stricken submarine. The injured survivors were transferred to the destroyer and sent to military hospitals for treatment, while the submarine returned under its own power to Primorsky Krai.[4] According to naval spokesman Igor Digaylo, the vessel was not damaged in the incident and radiation levels remained normal.[10]

Two principal explanations of the disaster have been advanced by naval experts and the media—an equipment failure or human error.

According to survivors, those affected by the gas release were caught off guard and may not have been alerted in time due to warning sirens sounding only after the gas had already begun pouring in. Some of the victims were reported to have been unable to don breathing kits before they suffocated.[16]

Igor Kurdin, a former Typhoon-class submarine commander and the current head of the St. Petersburg Submariners Club, attributed the high casualty count to the presence of a large number of civilian specialists on the submarine at the time of the accident. Seventeen of 20 people who perished in the accident were civilians. He noted that civilian observers would be untrained in the proper response to the release of the boat's firefighting gas, which would be preceded by a specific light and sound signal, after which all on board are supposed to put on oxygen masks to allow them to survive during the 30-minute period required to ventilate the compartments before they can be reopened. In addition, because the accident occurred at 8:30 pm, many of the civilian specialists and crewmen would likely have been asleep, and unable to don their oxygen masks in time.[17] The accident is the country's worst since the controversial 12 August 2000, sinking of the Russian nuclear submarine Kursk.

Mikhail Barabanov, editor-in-chief of Moscow Defense Brief, said the potential for accidental discharge of the fire-suppression system on Russian submarines is not unheard of, but this type of incident does not normally result in fatalities. However, Nerpa was carrying what he described as a "crowd of civilians" on board. The presence of the civilian shipbuilding contractors in addition to the military crewmen resulted in the vessel becoming "overcrowded". His estimation of the events that compounded the loss of life were: "the fire alarm failed to work, so passengers did not realize that the gas started to displace oxygen in the affected compartments."[18] Some suggested that not enough breathing kits had been available for the larger than usual number of people aboard, or that the civilians had not been properly trained in their use.[1] Survivors stated that some breathing apparatuses had not worked or had failed after only a few minutes; some of the dead were reportedly found still wearing their breathing kits.[15]